Cryogenic refrigeration device

ABSTRACT

A thermodynamic, regenerative-cycle refrigerating device including a compression space, a cooler, a regenerator and a cold finger formed as a cylinder with a displacer movable therein for defining an expansion space, the cold produced being transferred from the expansion space primarily through a thin cap at the end of the cylinder.

United States Patent Daniels [54] CRYOGENIC REFRIGERATION DEVICE [72] Inventor: Alexander Daniels, Briarcliff Manor,

[73] Assigneez U.S. Philips Corporation, New

York, NY.

[22] Filed: Dec. 29, 1969 [21] Appl. No.: 888,542

[52] US. Cl. ..62/6, 60/24 [51] Int. Cl. ..F25b 9/00 [58] Field of Search ..62/6; 60/24 [56] References Cited UNITED STATES PATENTS 1,675,829 7/1928 Smith ..60/24 51 Oct. 10,1972

Daniels ..60/24 3,218,815 11/1965 Chellis ..62/6 3,303,658 2/ 1967 Chellis ..62/6 3,314,244 4/1967 Green ..62/6 3,530,681 9/ 1970 Dehne 62/6 Primary Examiner-William J. Wye Attorney-Frank R. Trifari [57] ABSTRACT A thermodynamic, regenerative-cycle refrigerating device including a compression space, a cooler, a regenerator and a cold finger formed as a cylinder with a displacer movable therein for defining an expansion space, the cold produced being transferred from the expansion space primarily through a thin cap at the end of the cylinder.

10 Claims, 3 Drawing Figures PATENTEDUCI 1 01912 E I PIE/23 Fig. 2

Fig.

I N VE NTOR. ALE XANDER DAN I E LS Aer-mm CRYOGENIC REFRIGERATION DEVICE BACKGROUND OF THE INVENTION In refrigeration machines operating on a regenerative thermodynamic cycle, such as the Stirling cycle, there are'typically five interconnected elements, namely a compression space, acooler, a regenerator, a freezer, and an expansion space. Although ideally three elements (compression space, regenerator, and expansion space) are sufficient to explain the operation of such cycles, in all practical machines, the cooler and freezer elements have been added in order to effect adequate heat transfer between the gas in the compression and expansion spaces and the surroundings. The addition of the cooler and freezer was found necessary to compensate for the poor thermal contact and heat transfer capability between the working gas and the compression and expansion cylinders; a further shortcoming, particularly in large engines, is that the ratio of the surface area to corresponding volumes in the compression and expansion cylinder is low, thus providing even less efficient heat transfer areas.

In prior art machines it has been common to form the cooler with fins for air cooling, or with internal ducts for liquid cooling; the freezer is formed as a massive end plate that encompasses the end of the expansion cylinder remote from the compression space and a cylindrical skirt part that extends axially along the length of this cylinder, contacting a major part of the expansion cylinders outer surface, particularly the part defining the expansion space. This freezer member, generally made of copper for its good heat transfer properties, comprises a substantially large mass that must be cooled itself, before it can be an efficient conducting path for the transfer of cold.

The freezer configuration described above was the logical choice, since it was believed that all available surface area of the expansion cylinders side and end walls must be used to optimize cold transfer out of this expansion space. For use with such a freezer the cooperating displacer has a lower part containing a regenerator, an upper part, and gas flow ducts from the regenerator exiting between the upper and lower parts through the displacer side wall, whereby expanding gas will flow first along the side of the upper part adjacent the freezer, and then to the expansion space.

In the operation of the above devices, it has been found that the cold transfer through such massive freezer elements has been generally what was calculated and was so accepted as optimum, despite the shortcoming of a substantially long cool-down period. In one typical refrigerator, as much as ten minutes elapses as the time required for cooling the large mass of the entire freezer before the device can operate at a design temperature level of 77 K. In applications where a short cool-down time is called for, these devices are obviously less desirable or unusuable, as where a device provides the refrigeration to cool an infra-red detector carried by a military plane. Ordinarily the refrigerator would not be run continuously; however when circumstances called for the detector to operate, it would be critical for the refrigerator to reach its operating conditions in a very short time. The inherently-high weight factor of these large freezers is a further undesirable feature.

SUMMARY OF THE INVENTION The present invention comprises a structure significantly different from all known prior art refrigerators operating on a thermodynamic, regenerative cycle, and in using this invention the cool-down period to reach operating temperature is greatly reduced over known devices. This has been achieved by a simplification of the refrigerator structure, namely the elimination of the freezer, which is the element that consumes so much time to cool-down during the start-up period of operation. More specifically, the new refrigerator is a V regenerative-cycle apparatus having a housing defining therein interconnected compression and expansion chambers of variable volume and different average temperatures, and a regenerator between the chambers. A cold finger portion of the housing is formed as a cylindrical body having a first end in communication with the compression chamber and, a remote end with the reciprocally movable displacer therein, defining the expansion chamber. Also provided is a means closing and sealing the remote end, with the cold produced being transferred out of the expansion chamber substantially entirely through the end closure, which preferably is a thin, flat cap defining a circular surface area.

It has been found that the surface area of the cap at the end of the expansion cylinder, is sufficient for the transfer of cold from the expansion space, and accordingly, that the additional surface area of prior art freezers along the side walls of the expansion cylinder, is unnecessary. Although the elimination of metal forming the freezers side walls reduces the available surface areas for cold transfer and corresponding rate of cold transfer from the expansion space, the reduced mass of metal has nevertheless resulted in the significant and unexpected great reduction in cool-down time. The new refrigerators reached operating temperature in a very short time, as much as three times faster than in comparable prior art machines. Furthermore, these new devices were able to continue transferring adequate quantities of cold through the thin closure means as was required. It should be added that the present invention has particularly good applicability in small machines where the ratio of expansion-cylinder surface area to expansion volume is greater than in large machines. Furthermore this invention is applicable in various other regenerative-cycle devices such as those designated Gifford-McMahon, Vuilleumier, and Solvay.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of a prior art device including a standard freezer,

FIG. 2 is a partial sectional view of the present invention, and

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to demonstrate the very substantial structural difference of the new invention over the prior art, FIG. 1 is provided disclosing a partial view of a typical prior art regenerative cycle refrigerator 10. The housing 11 has compression piston 12 reciprocally movable therein, defining the variable volume compression chamber 13, which is surrounded by an air-cooled cooler 14. A cylindrical cold-finger 15 having one end in communication with the compression space, extends upward as shown, and is sealed at the top by freezer 16 having head part 17 and sleeve or skirt part 18. The cold-finger and the reciprocally movable displacer 19 therein define the variable volume expansion space 20. The compression piston 13 and the displacer 19 are driven, out-of-phase with each other, respectively by rods 21 and 22 connected to a drive means not shown.

Disposed within the center part of the displacer 19 is a regenerator 23; however the invention is equally applicable to a device having an alternative form of regenerator external of the displacer. Spaced between upper part 19a of the displacer and the regenerator 23 are ducts 25 exiting at the side wall of the displacer, and through which the working gas passes into the annular space 25a and thence to expansion chamber 20, with the cold produced in the annular space and in this chamber being transferred via the contacting wall surfaces of the freezers cylindrical skirt part 18 extending axially along the cold-finger, and its circular head part 17. When the mass of these walls is finally cooled to the device's operating temperature, then usable cold is available for external purposes.

FIG. 2 discloses one preferred embodiment 10a of the present invention, which is similar to FIG. 1, as regards the housing, piston, displacer, regenerator, and cooler; however, the freezer 16 (FIG. 1) has been eliminated. Here a thin cap 26 formed basically as a disc closes and seals the top end of the cold-finger 15. Consistent with the invention concept of minimizing the mass about the expansion space for optimizing cool-down time, the cap 26 has a nominal thickness, sufficient only to withstand the internal pressure and maintain the seal of the cold-finger. In the device shown, the cap thickness is about 0.1 inches, in refrigerator having a displacer stroke of about 0.3 inches and diameter of about 0.4 inches.

The surface area operable to transfer cold out of the expansion space is merely the circular area under capv 26, defined by [1rD /49 in contrast to the much greater area in the prior art defined by [1rD /4] plus the additional area of sleeve 18, [rrDX sleeve length]. The preferred displacer has an internal regenerator 23 and duct apertures 25b in the end plates 25c and oriented for the gas to flow axially into the expansion space. This displacer eliminates a certain volume of dead space occupied by upper part 19a of the prior art displacer, allowing a reduction in size and mass of this component.

It has been found in operating refrigerators having cold-fingers of the above dimensions, that a temperature of 77 K. could be reached in 3 minutes with the new invention as compared with the time of 10 minutes for comparable prior art devices. In these examples the temperature drop was from normal room temperature of about 300 K., and resulted in production of about 1 watt of cold at this 77 K. temperature. Corresponding results are achievable when the present invention is applied to refrigerators with other dimensions, and with varying configurations, such as a crowned instead of flat displacer 19 of FIG. 1 having ducts 25 from the internal regenerator exit at the sides of the displacer rather than at the top. This invention is further applicable to the cold-finger portion of refrigerators having the compressor unit separated from and driven independently of the cold-finger.

lclaim:

1. In a thermodynamic, regenerative-cycle refrigerator operable to cool a compressible gas which gas can then receive thermal energy from a mass to be cooled, the refrigerator having a housing, a piston reciprocally movable in the housing and defining a variable volume compression space, a cold-finger comprising a cylindrical member with a first end in communication with the compression space and a remote end, a displacer reciprocally movable in said member and defining therein a variable volume expansion space of lower average temperature than the compression space, and means for driving the piston and displacer, a regenerator disposed between the compression and expansion spaces, with said compressible gas disposed within said spaces and cyclically moved therebetween, the gas being expanded and cooled in the expansion space, and closure means closing and sealing said remote end and thus defining a boundary of the expansion space, the thermal energy being transferrable into the cooled gas within the expansion space substantially entirely through said closure means.

2. In a thermodynamic, regenerative-cycle refrigerator operable to cool a compressible gas which gas can then receive thermal energy from a mass to be cooled, the refrigerator having a housing, a piston reciprocally movable in the housing and defining a variable volume compression space, a cold-finger comprising a cylindrical member with a first end in communication with the compression space and remote end, a displacer reciprocally movable in said member and defining therein a variable volume expansion space of lower average temperature than the compression space, and means for driving the piston and displacer, a regenerator disposed between the compression and expansion spaces, with said compressible gas disposed within said spaces and cyclically moved therebetween, the gas being expanded and cooled in the expansion space, and closure means closing and sealing said remote end and thus defining a boundary of the expansion space, the thermal energy being transferrable into the cooled gas within the expansion space substantially entirely through said closure means, wherein the said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member wherein the said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member.

3. A refrigerator as defined in claim 2 wherein said thermocynamic cycle is a Stirling cycle.

4. A refrigerator as claimed in claim 2 wherein said closure means further comprises a flange for securely engaging the closure means to the remote end of said member, the flange being short relative to the length of said cylindrical body.

5. In a thermodynamic, regenerative-cycle refrigerator operable to cool a compressible gas which gas can then receive thermal energy from a mass to be cooled, the refrigerator having a housing, a piston reciprocally movable in the housing and defining a variable volume compression space, a cold-finger comprising a cylindrical member with a first end in communication with the compression space and a remote end, a displacer reciprocally movable in said member and defining therein a variable volume expansion space of lower average temperature than the compression space, and means for driving the piston and displacer, a regenerator disposed between the compression and expansion spaces, with said compressible gas disposed within said spaces and cyclically moved therebetween, the gas being expanded and cooled in the expansion space, and closure means closing and sealing said remote end and thus defining a boundary of the expansion space, the thermal energy being transferrable into the cooled gas within the expansion space substantially entirely through said closure means, wherein the said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member, and wherein said closure means is formed of a metal such as copper having good thermal conductivity, and has thickness substantially only sufficient to withstand the pressure within said expansion chamber. 6. In a thermodynamic regenerative-cycle refrigerator operable to cool a compressible gas which gas can then receive thermal energy from a mass to be cooled, the refrigerator having a housing, a piston reciprocally movable in the housing and defining a variable volume compression space, a cold-finger comprising a cylindrical member with a first end in communication with the compression space and a remote end, a displacer thermal energy being transferrable into the cooled gas within the expansion space substantially entirely through said closure means, wherein the said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member, the refrigerator having a refrigeration output or thermal energy absorption power of approximately 1 watt, and a cool-down time from about 300 K. to 77 K. of less than 4 minutes.

7. A refrigerator as defined in claim 2 wherein the displacer has a diameter of approximately 0.4 inch and a stroke of approximately 0.3 inch long, and the refrigeration output is about 1 watt at 77 K.

8. In a thermodynamic regenerative-cycle refrigerator operable to cool a compressible gas, which gas can then receive thermal energy from a mass to be cooled, the refrigerator operable with first means providing a compressed working medium, the refrigerator having a housing including a cold-finger which comprises a cylindrical member having a first end in communication with the compressed medium and remote end, a displacer reciprocally movable in the member and defining at the remote end of the member a variable volume expansion space having lower average temperature than said medium in the first means, second means for driving said displacer, a reg enerator connected between he'first means and he expansion chamber, and'closure means closing and sealing the remote end of the member, the refrigeration produced such that thermal energy transferrable from said mass into the expansion chamber substantially entirely through said closure means.

9. A refrigerator as defined in claim 8 wherein sai closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member.

10. A refrigerator as defined in claim 8 wherein the thermodynamic cycle is the Stirling cycle.

i e a a:

7%? UNITED STATES "PATENT. QFFICE CERTIFICATE OF CORRECTION -.Patent NO. 3,696,626 Dated October 10, 1972 Inventor (s) ALEXANDER DANIELS It is certified that error appears in the above-identified patent and that said Letters Patent-are hereby corrected as shown below:

Col. 3, line 46, "49" should be -4] Signed and sealed this 2 'rch day of April 1973.

(SEAL) Attest: I-BDWARD M. FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer 7 Commissioner of Patents 

1. In a thermodynamic, regenerative-cycle refrigerator operable to cool a compressible gas which gas can then receive thermal energy from a mass to be cooled, the refrigerator having a housing, a piston reciprocally movable in the housing and defining a variable volume compression space, a cold-finger comprising a cylindrical member with a first end in communication with the compression space and a remote end, a displacer reciprocally movable in said member and defining therein a variable volume expansion space of lower average temperature than the compression space, and means for driving the piston and displacer, a regenerator disposed between the compression and expansion spaces, with said compressible gas disposed within said spaces and cyclically moved therebetween, the gas being expanded and cooled in the expansion space, and closure means closing and sealing said remote end and thus defining a bounDary of the expansion space, the thermal energy being transferrable into the cooled gas within the expansion space substantially entirely through said closure means.
 2. In a thermodynamic, regenerative-cycle refrigerator operable to cool a compressible gas which gas can then receive thermal energy from a mass to be cooled, the refrigerator having a housing, a piston reciprocally movable in the housing and defining a variable volume compression space, a cold-finger comprising a cylindrical member with a first end in communication with the compression space and remote end, a displacer reciprocally movable in said member and defining therein a variable volume expansion space of lower average temperature than the compression space, and means for driving the piston and displacer, a regenerator disposed between the compression and expansion spaces, with said compressible gas disposed within said spaces and cyclically moved therebetween, the gas being expanded and cooled in the expansion space, and closure means closing and sealing said remote end and thus defining a boundary of the expansion space, the thermal energy being transferrable into the cooled gas within the expansion space substantially entirely through said closure means, wherein the said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member wherein the said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member.
 3. A refrigerator as defined in claim 2 wherein said thermocynamic cycle is a Stirling cycle.
 4. A refrigerator as claimed in claim 2 wherein said closure means further comprises a flange for securely engaging the closure means to the remote end of said member, the flange being short relative to the length of said cylindrical body.
 5. In a thermodynamic, regenerative-cycle refrigerator operable to cool a compressible gas which gas can then receive thermal energy from a mass to be cooled, the refrigerator having a housing, a piston reciprocally movable in the housing and defining a variable volume compression space, a cold-finger comprising a cylindrical member with a first end in communication with the compression space and a remote end, a displacer reciprocally movable in said member and defining therein a variable volume expansion space of lower average temperature than the compression space, and means for driving the piston and displacer, a regenerator disposed between the compression and expansion spaces, with said compressible gas disposed within said spaces and cyclically moved therebetween, the gas being expanded and cooled in the expansion space, and closure means closing and sealing said remote end and thus defining a boundary of the expansion space, the thermal energy being transferrable into the cooled gas within the expansion space substantially entirely through said closure means, wherein the said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member, and wherein said closure means is formed of a metal such as copper having good thermal conductivity, and has thickness substantially only sufficient to withstand the pressure within said expansion chamber.
 6. In a thermodynamic regenerative-cycle refrigerator operable to cool a compressible gas which gas can then receive thermal energy from a mass to be cooled, the refrigerator having a housing, a piston reciprocally movable in the housing and defining a variable volume compression space, a cold-finger comprising a cylindrical member with a first end in communication with the compression space and a remote end, a displacer reciprocally movable in said member and defining therein a variable volume expansion space of lower average temperature than the compression space, and means for driving the piston and displacer, a regenerator disposed between the compression and expansion spaces, with said compressible gas disposed within said spaces aNd cyclically moved therebetween, the gas being expanded and cooled in the expansion space, and closure means closing and sealing said remote end and thus defining a boundary of the expansion space, the thermal energy being transferrable into the cooled gas within the expansion space substantially entirely through said closure means, wherein the said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member, the refrigerator having a refrigeration output or thermal energy absorption power of approximately 1 watt, and a cool-down time from about 300* K. to 77* K. of less than 4 minutes.
 7. A refrigerator as defined in claim 2 wherein the displacer has a diameter of approximately 0.4 inch and a stroke of approximately 0.3 inch long, and the refrigeration output is about 1 watt at 77* K.
 8. In a thermodynamic regenerative-cycle refrigerator operable to cool a compressible gas, which gas can then receive thermal energy from a mass to be cooled, the refrigerator operable with first means providing a compressed working medium, the refrigerator having a housing including a cold-finger which comprises a cylindrical member having a first end in communication with the compressed medium and remote end, a displacer reciprocally movable in the member and defining at the remote end of the member a variable volume expansion space having lower average temperature than said medium in the first means, second means for driving said displacer, a regenerator connected between the first means and the expansion chamber, and closure means closing and sealing the remote end of the member, the refrigeration produced such that thermal energy transferrable from said mass into the expansion chamber substantially entirely through said closure means.
 9. A refrigerator as defined in claim 8 wherein said closure means has a thermal energy transfer surface defined generally as a circular area bounding only one end of said member.
 10. A refrigerator as defined in claim 8 wherein the thermodynamic cycle is the Stirling cycle. 